It is known to provide a one way gate which spans a pair of parallel side panels so as to allow animals to pass between the panels in one direction only, with the intention of preventing the animals from turning an passing back in the opposite direction. Such gates are typically used for pigs to manage the pigs between pens so that they can access a second pen from a first pen but cannot turn around and go back. The gate should not inhibit the animals from moving in the required direction. The gate can form part of an alley but more commonly the panels are placed in an opening in a fence line between the two pens with the panels at right angles to the fence line.
It is known that such a gate is formed by a series of depending fingers at spaced positions across the space between the panels and carried on a top rail so that each finger can pivot about a horizontal axis defined at the rail allowing the lower end of the finger to lift to a position where the animal can pass underneath the raised fingers and underneath the rail. The fingers can pivot from a hanging position only in one direction to prevent passage in the reverse direction. The animal lifts enough of the fingers to allow it to pass simply by pushing against the fingers. The intention is that it is sufficiently difficult for the animals to lift the fingers to prevent passage in the reverse direction even.
However it is found that some pigs can get back in the reverse direction by working on lifting the fingers until they achieve a condition where enough fingers are lifted which may combine with the passage of another pig in the intended direction thus allowing a pig to escape. This is of course unacceptable in a management system which relies on the reverse passage of none of the pigs. The pigs tend to try extensively to pass in the reverse direction because they are naturally curious and in some cases the food or water may be in the first pen giving a higher incentive.